Direct-writing oscillograph



June 8, 1965 F. F. OFFNER 3,133,651

DIRECT-WRITING OSCILLOGRAPH Filed Feb. 8, 1965 3 Sheets-Sheet 1 INVENIOR FrankL Ln F Off/ Yer ATTORNEY S June 8, 1965 Filed Feb. 8, 1963 F. F. OFFN ER 3,188,65 1

DIRECT-WRITING OSCILLOGRAPH 3 Sheets-Sheet 2 INVENTOR Fran/V107 F. 07"1 nerlimb, JW x, PM)

ATTORNEYS June 8, 1965 F. F. OFFNER 3,188,651

DIRECT-WRITING OSCILLOGRAPH Filed Feb. 8, 1965 5 Sheets-Sheet 3 Han/din F Offner MJWYQPCUJEW ATTORNEYS United States Patent 3,188,651 DIRECT-WRITING OSCELLOGRAPH Franklin F. Ofiner, 1890 Telegraph Road, Deeriield, ill. Filed Feb. 8, 1963, Ser. No. 257,121 7 Claims. (Ql. 346-417) The present invention relates to oscillographs or recorders of the direct writing type and more particularly to an improved construction wherein one obtains a rectilinear record.

In the past, direct-writing osclllographs have usually been of the curvilinear writing type as disclosed, for example, in applicants previous United States patents, Nos. 2,150,729, 2,262,958 and 2,688,729. Rectilinear inkwriting recorders have been devised, employing linkage systems for sliding the pen arm back and forth, approximately in accordance with the arc distortion, in order to maintain a rectilinear trace. Other rectilinear systems have been devised, using, for example, heat and electric sensitive paper, in which the paper passes over a sharp edge, the stylus being a second sharp edge running along the paper, thus producing a rectilinear recording.

The advantages of a rectilinear recorder, as compared with one of the curvilinear type are obvious, since it permits the record to be read in ordinary cartesian co-ordinates. The systems of obtaining rectilinear records up to now have all suilered from various defects. Linkage systems are complex, offer friction and may suffer from lost motion due to ventual wear. Systems employing electrical or heat sensitive paper do not provide as satisfactory recordings as ink records, and in addition employ expensive and fragile recording media.

The general object of the present invention is to thus provide an improved oscillograph of the direct-writing type, '1.e. one producing an inked record, wherein the record itself is a rectilinear one with its inherent advantages but which avoids the disadvantages of prior art constructions.

The object is accomplished by means of a novel and improved stylus construction of the stylus and its supporting structure is such that no linkage system is required to be used intermediate the rotatable ga-lvanometer coil element and stylus point for converting rotary motion of the coil into rectilinear motion of the stylus point. Moreover, the improved construction has the advantage that no restoring spring need be associated with the galvanometer coil since a self-balancing servo-system is employed and the galvanometer coil is supplied with current only when there is a change in input signal. The improved construction also has the advantage that a derivative component of the signal can be employed in the servo system to dampen and hence, stabilize operation of the system under conditions which otherwise might well lead to spurious oscillations of the stylus and its trace thus producing errors in the latter. A further advantage is that the accuracy of positioning the stylus correctly in accordance with the input signal is rendered independent of any variations in the magnetic field associated with the movable coil element of the galvanometer unit.

In general, the improved construction includes a galvanometer coil adapted to be energized by an amplified input signal, the coil being arranged for rotation about its axis dependent on the amplitude of the signal. Mounted for rotation with the coil is a stylus arm having a recording pen located at the outer end thereof. This stylus pen moves rectilinearly along a rectilinear member placed transverse to the path of movement of the record paper and the outer end of the arm includes also a contact member which establishes a spring loaded sliding contact with a potentiometer resistance element which extends along the transversely placed rectilinear member. The

amount of voltage signal picked up at any time depends upon the position of the contact member on the resistance element and this voltage is used as a feedback voltage to balance the signal voltage at the input. No restoring spring is used in conjunction with the galvanometer coil and the latter receives current essentially only when there is a change in the input signal.

The foregoing as well as other objects and advantages of the invention will become more apparent from the following detailed description of some preferred embodiments thereof and from the accompanying drawings which illustrate the same. In these drawings:

FIG. 1 is a combined electrical schematic and somewhat diagrammatic view of the rectilinear recording systern;

FIG. 2 is a partial top plan view of the galvanometer and stylus structure in association with the movable recording tape or chart;

FIG. 3 is a fragmentary view partly in section illustrating a modifiedconstruction for the stylus supporting structure;

FIG. 4 is also a fragmentary view partly in section illustrating a further modification for the stylus supporting structure;

FIG. 5 illustrates a modified circuit arrangement for obtaining the derivative damping characteristic included in the circuit of FIG. 1;

FIG. 6 illustrates another modified circuit arrangement for obtaining this derivative damping characteristic;

FIG. 7 is an electrical schematic for the main amplifier unit employed in the FIG. 1 system;

FIG. 8 is an electrical schematic for the feedback amplifier unit employed in the FIG. 1 system;

FIG. 9 is an electrical schematic for deriving an additional feedback signal for insuring stability of operation at higher signal frequencies; and

FIG. 10 is an electrical schematic illustrating a modified circuit arrangement for the main signal amplifier shown in FIG. 7.

With reference now to the drawings and to FIGS. 1 and 2 in particular, the improved direct-writing oscillograph in accordance with the invention includes a stylus l which is arranged to be shifted transversely in a rectilinear manner across the upper surface of a continuous tape 2 moving in the direction indicated in FIG. 1 by the arrow. This tape is supplied from a feed roll 3 and is advanced between drive rolls 4 that can be driven by an electric motor 5. One suitable type of paper drive is disclosed in my United States Patent No. 2,977,112 granted March 28, 1961. Ink is supplied to stylus 1 through flexible tubing 6 which is connected to a supply source for the ink such as an inkwell 7. If desired, the inkwell may be mounted for vertical adjustment in a sleeve 8 so as to vary the height above the point of the stylus and hence, provide a variable pressure to the ink as may be required to obtain a particular type of line. Alternatively, the ink in inkwell 7 may be placed under pressure, if required, in order to obtain a sufiiciently dense line.

The stylus .1 is carried at the outer, free end of one leg of .a V-shaped flat spring 9 and included with the stylus is an electrical contact member 1%) which slidably engages an elongated, straight resistance wire 11 that is secured to and along an elongated rectilinear insulating member 1'2 extending transversely across the upper surface of the moving tape 2 but with sufiic-ient clearance as indicated in FIG. 1 so as not to interfere with movement of the tape. The other leg of the V spring 9 is rigidly secured to the outer end of an elongated support arm 14 and is for all purposes virtually immovable. The V spring 9 serves to continuously urge the contact member 10 into a sliding engagement with the resistance Wire 11 as the support arm 14- moves back and forth in an arcuate sweep about its rearward pivotal support structure, thus assuring a rectilinear displacement of the stylus 1 across the tape 2 in a direction transverse to its direction of longitudinal movement.

The rear end of support arm .14 is provided with a transversely extending pivot shaft 15 whichfis pivotally mounted in a cradle .16 for rotation about a horizontal axis. This provides for some degree ofvertical pivotal movement of the support arm 14, and a leaf type spring 17 arranged on the cradle 16 has its outer free end arranged so as to bear downwardly upon the upper surface of support arm 14 thus biasingjthe stylus 1 downwardly into a'firm, ink writing'engagement with the surface of tape 2. a

The cradle 16 is, in turn, secured to the upper end of a vertical shaft 18 which is mounted at its lower end to an electrical coil 19Mwhich is arranged to rotate about a vertical axis defined by upper and lower jew-elled pivot bearings 20, 21 which are in vertical alignment with the axis of shaft 18,, The electrical .coil 19 is arranged to rotate in a magnetic field produced by two permanent magnets 22, 23 and a stationary iron core 24 located inside of the coil 19.. The m-agnetic path between the permanent magnets 22, 23 is completed by the usual soft iron yoke, not shown. The electrical parts 19, 22, 23 and 24 constitute a galvanometer of generally conventional structure and may be departed from in various particulars so as to effect the desired result which is an angular displacement of the support arm 14 about a vertical axis through the movable coil assembly depending on the current which is passed through galv-anometer coil w. However, it will be noted that .no restoring force such as a spring, is used in conjunction with the movable coil 19 to restore ,i-tto its initial, zero position when the current to coil 19 is interrupted.

The electrical power to actuate galvanometer coil 19 and hence, to'drivet-he stylus 1 back and forth in a rectilinear manner across the moving tape 2,, is furnished byfamplifier 26. This amplifier may be any of a wide variety of types. As illustrated, it is an amplifier having a common, grounded terminal 27, an output terminal 28, Iand differential input terminals 29,; 3Q. That is, with this amplifieiconfiguration, the output signal generated terminals 291, 30. Thus, the signal at output terminal 28' becomes a function of the signal at terminal 29 and the' signal at terminal 39, If, as a special case, and one which is most useful, amplifier 26is a true differential, linear amplifier, the output signal at terminal 28 is equal to the signal at terminal 29 minusthe signal at termianl 3%.

It is important to note, however, that the operation of the improved recording device in accordance with the present invention does not depend upon amplifier 26 being either a true differential amplifier, nor on its having linear amplification. It is desirable, however, that amplifier 26 have a high amplification factor, and that it provide a large available power output, if it be desired to have a rapid response from the oscillograph system.

The input signalto amplifier 26. is applied from the signal source to be recorded, at terminal 31 and is connected to input terminal 29 of the amplifier by Way of an attenuator unit 3 2,if some attenuation in input signal is desirable or necessary. The output from amplifier 26, i.e. at terminal 2-8 and the common terminal 27 is con nectedbyleads 33, 34 to the ends of the galvanometer coil 19.

A current is passed through the resistance wire 11 by connecting one end thereof to a source of voltage indicated by'term-inal 35 and by conneotingthe opposite end to ground which is also the potential of the common terminal 27 of amplifier 26, This will produce a voltage dropacross the resistance 11 which will vary progressively from one end thereof to the other. A portion of this voltage drop is picked upby contact member 10 associated with stylus 1 and the amount of this voltage will depend upon the transverse position of stylus 1 on the tape 2. This voltage drop is led back through suitable connections indicated schematic-ally by conductor 36 to the input terminal 37 of a second amplifier unit 38. Am plificr uni-t 355 is of a type similar to amplifier 26. This is, it has two input terminals 37, 39 a common grounded terminal do and output terminal 41. The relationship between the output signal from terminal 4 1 and the input signals from terminals 37-, 3% is similar to the relationship o-f th-eroutput signal from amplifier 26 to thefinput- In the case of amplifier 38, it;

signals of that amplifier. is desirable, however, that the output at terminal 41 should e a linear function of the signal applied to input terminal Amplifier unit 38 serves two functions; it amplifies a fedback signal as picked up by contact member 10, so that an amplified signal is available at theoutput terminal 41, for further use asto be later described. Amplifier unit 38 has, however, a further and more essential function: it

provides a phase lead signal, necessary for stabilization of. the servo system through which the stylus 1 is positioned. Due to the inertial lag of the, galvanometer. sys-.. tem, combined with other lags of the system, the. stylus positioning signal applied to coil 19, and required to maintain stylus 1 at its desired position would cause unstable oscillations if sufficiently large amplification were employed to obtain the desired rapid response. To compensate for this inertial and other lags, and anticipatory signal is required. This is obtained by amplifier unit-38, through the use of partially integrated feedback. The feedback signal is obtained fromv output terminal 41- through resistor 42. The signal fromresistor 42 -is applied across capacitor 43, partially integrating it before being applied as a feedback signal to the second input terminal 39. Through the well known action of integrated feedback, as disclosed in US. Reissue Patent No. 24,809, the signal developed at terminal contains a derivative component. of the signal applied to input terminal 37. This derivative component provides the neces: sary anticipatory component, thus permitting stabilization of the servo system. 7

The output signal from terminal 4-1 may be applied to an attenuator 44. permitting the application of any desired fraction of the output signal to input terminal 30 of amplifier 26. This permits the reduction of feedback signal, thus giving a higher sensitivity to the over-all recording system. Normally, the attenuator 44 willonly be used to attenuate the feedback signal when attenuator 32 is at its uppermost position; that is, providing no attenuation of the signal appliedto terminal 29 'from signal input terminal 31.

The reason that attenuation of the output signal from, terminal 41 by attenuator 44 increases the sensitivity is the following. Displacement of the stylus actuated connet amplification of amplifier unit 38.

applied to terminal 29. Assuming that amplifier unit 26 is of the linear differential type, the. output signal at terminal 41 will be exactly equal to the input signal at terminal 29. If, however, theoutput signalfrom terminal 41 is attenuated to one-half its value by'the attenuator unit 44,

then the contact member 10 must move twice as far, produclng twice the input signal to terminal 37, in order to produce the same feedback signal at terminal 300i arnplifier unit 26. This, therefore, shows that attenuating the feedback signal by attenuator unit 44 gives a proportionate increase in the over-all sensitivity of the recording system.

As contact member slides back and forth on the slidewire resistance 11, it may encounter small particles of non-conducting material, rough spots on the Wire itself, or for other reasons, it may make imperfect contact instantaneously with the slide wire resistance 11. The purpose of capacitor 45 connected to conductor which leads to amplifier input terminal 37 and to ground is to minimize the effect of such disturbances. Consider that contact member 10 momentarily fails to make contact with the slidewire resistance 11 as it shifts from one to another position on the latter. This would normally cause a large change in the input signal to amplifier 38, producing a still larger input to amplifier 26, giving a momentary very large surge of current to the coil 19. This large pulse of current can cause an unstable oscillation of the stylus support arm 14. The result may be that the stylus 1 completely moves off of the slidewire 11, and fails to return. The function of capacitor is to momentarily retain the last potential existing at contact member 18. Capacitor 45 may be fairly large in value, at least several hundred microfarads, without aifecting the speed of response of the recorder system. This is because contact 10 normally makes a very low resistance contact to the slidewire resistance 11, so that capacitor 45 follows essentially instantly the potential picked up at contact In. If, however, contact 10 loses engagement with the slidewire resistance 11, then the impedance at terminal 37 is very high, so that capacitor 45 Will discharge only slowly. Thus, contact 10 will have the time to travel to a new position, and take its proper potential from resistance 11, without any large, uncontrolled signals being applied to the galvanometer coil 19.

A resistor 46 has one end connected to amplifier input terminal 37 and the other end connected to a variable potential divider 47 in the form of a variable resistance connected between ground and a source of potential applied to terminal 48. The resistor 46 has a very high ohmic value and is employed to balance out any input currents which may exist at terminal 37, and establish at this latter terminal an equilibrium potential corresponding to an approximately central position of contact 10 on slidewire resistor 11. The purpose of this is to insure that if contact 10 loses electrical engagement with resistance wire 11, stylus 1 will return to approximately its central position on the tape 2, in the absence of signals applied to terminal 29 of amplifier unit 26. This then causes the stylus 1 to return to approximately its central position, returning contact 10 to slidewire resistance 11.

It is desired that stylus 1 be in a pre-assigned position on the tape chart 2, in the absence of signals applied to terminal 29 of amplifier unit 26. This position is fixed by a potential selected from a variable potential divider 49 which is connected to a source of potential between ground and terminal 56. The potential taken off the divider 49 is applied to resistor 51 and thence to input terminal 39 of amplifier unit 38. If the latter is of the true differential design and if the potential applied to terminal 39 corresponds to the potential on slidewire resistance 11 at the desired rest point of stylus 1, amplifier unit 38 will have no output at this position of stylus 1, and the stylus will therefore remain at the desired position in the absence of an input signal to terminal 29.

The preceding description has described the essentials of the electronic functioning of one embodiment of the invention. Mechanically it is seen that if contact member 10 slides along the straight line established by the rectilinear resistor unit 11, then sylus 1 must also necessarily move in a rectilinear fashion transversely across the chart tape 2. This is illustrated more completely in FIG. 2. The solid line drawing of the support arm 14, stylus 1 and the V-spring 9 therebetween depicts the stylus 1 and contact member 10 in the central position across the tape 2 and resistor wire 11 respectively, it being 5 noted that the angle between the two legs of the V spring 9 is at a minimum. As arm 14 rotates from this center position to one side or the other, such as indicated by the dash-dot line representation, this angle opens due to the spring action thus keeping the contact member 10 engaged with the resistor wire 11 and causing stylus 1 to move along a rectilinear path.

FIGS. 3 and 4 illustrate modified constructions for the stylus and particularly its connection with the outer end of arm 14 so as to assure a rectilinear movement of the stylus as the arm 14 rotates as a result of current applied to coil 19 of the galvanometer system.

With reference to FIG. 3, it will be seen that the stylus 1' is carried by an arm 52 which is pivotally connected to a bracket 53 secured rigidly to the outer end of arm 14'. A loading spring 54 under compression is located in an axial recess 55 in arm 14', and the outer end of spring 54 bears against the stylus support arm 52 which thereby urges the contact member 16 against the slide- Wire resistance 11.

FIG. 4 shows a further modification for the stylus which uses a tension spring to hold the contact member against the slidewire resistance element. In this view, stylus 1 is mounted on an arm 56 pivotally secured to a bracket 5'7 secured rigidly to the outer end of the support arm 14". A tension spring 58 has one end anchored in an axial recess 59 in the end of arm 14" and the opposite end anchored on arm 56 intermediate its ends, thus exerting a pulling action on arm 56 which tends to hold the contact member 10" in engagement with the slidewire 11" and again causing the stylus 1" to move rectilinearly across the tape 2. The advantage of the construction according to FIG. 4 is that the slidewire resistor unit it" and its insulation support will not obscure the record written by the stylus in the vicinity of the stylus point itself since these elements will then be located over a portion of the tape not yet recorded upon. This advantage does not obtain with the construction shown in FIGS. 1 and 3.

Other modifications of the arrangement shown in FIGS. 1 and 2 are also possible. For example, different methods for obtaining an anticipatory signal, other than the use of a feedback amplifier 38, may be employed. One such method is to employ the potential generated by conductors moving in the magnetic field of the galvanometer unit. These conductors may be either the actual driving coil of the galvanometer, in a method described in applicants co-pending United States patent application, Serial No. 790,498, filed February 2, 1959, or by a separate coil rotating along with the driving coil 19.

The basic circuit for the former method is illustrated in FIG. 5. Portions of this circuit bearing corresponding numerals to those of FIG. 1 have a corresponding function. It is seen here that the coil 19 is made one arm of a Wheatstone bridge, the other arms being balancing resistor 69, and ratio arms composed of the tWo portions of a voltage divider 61, above and below the contact point. The primary 62a of transformer 62 is placed across the bridge, as shown. When the bridge is balanced for direct current, essentially no current will flow through the primary winding 62a, except that due to the back generated in coil 19' due to its motion in the magnetic field. Therefore, the voltage induced in the secondary winding @212 is proportional to the back EM.F., and therefore, proportional to the velocity of rotation of coil 19'. It is thus equivalent to the differentiated signal picked up from the slidewire resistor 11 in the method illustrated in FIG. 1, the differentiated signal being also proportional to the velocity of the stylus travel, and thus to the rotational velocity of coil 19'. The signal from the transformer secondary 62]) may thus be placed in series with the signal from the slidewire resistor 11 as picked up from conductor 36, as shown, and thus adds the desired derivative component to the input terminal 3d of amplifier as.

An alternative arrangement, as shown in FIG. 6, which tact-member 10, then the back of'the coil used.

for the anticipatory signal will anticipate the differentiated signal picked up from contact 10 by the amount of the time delay which may be caused by such lost motion. The velocity signal thus produced can, therefore, havea greater stabilizing effect than the signal obtained by, differentiating-the voltage picked upfrom contact 19. As between the circuit arrangements of FIGS. and 6, that of FIG. 5 has the advantage of not requiring a separate velocity. signal producing coil, with its attendant need for flexible leads connetced to the rotating coil body. However, it requires the careful balancing of the bridge, in order to avoid the effects of direct signal components being added to the velocity component from transformer 62. The

rectly coupled to a second differential stage using PNP transistors 66, 67, in a complementary symmetry circuit. When the collector at transistor 66 is at zero potential,

then neither of the transistors which follow, namely, a

PN'P transistor 68 or an NPN transistor 69 will draw appreciable current. Therefore, no base current is provided for-power output stage transistors 70 which is of the NPN type and 71 which is of the PNP type. As a result, there is no output current provided through amplifier output terminal 28 to the galvanometer coil 19. Assume, however, that the collector of transistor 66 is negative with respect to the common'point; This will cause current to flow through transistor :68, 1 and amplified current through output transistor '70. If the collector of transis tor 66 becomes positive, similarly a current will be drawn by transistor 69, and an amplified current by output transistor 71, producing a current flow through galvanometer coil 19 of the opposite. sense. The functioning of a transistor circuit of this type is now fairlywell understood in the art, but is further explained in applicants I co-pending application'Seria l No. 790,498 filed February 2, 1959;

The feedback amplifier unit 38 may conveniently be essentially the same as the first part-of the amplifier unit shown in FIG. 7 including only the first four transistors of that circuit. This is depicted in FIG. 8, the fourtransisters being numbered 64, 65', 66' and 67 to distinguish them fro'm the transistors in the FIG. 7 circuit. The 'output terminal of the amplifier 38 is indicated by numeral 41 and the input terminals by numerals 37 and 39 in accordance with the usage in FIG. 1.

In the embodiments of the invention \which have been described, feedback of various types is employed,- including the output voltage of amplifier unit 26, obtained from $5 terminal '28, backthrough the input of amplifier 26- through terminal 30. if an attenuator 44 isemployed in conjunction with the output of the feedback amplifier unit 38, as in the circuit of FIG; 1, the additional-feedback should be'made, as shown, to the unattenu ated sig n al at the upper end of the attenuator unit 44,i.'e. witha direct connection .to the amplifier output terminal 41.

The purpose of the additional-feedbackis to limit the" overall gain ofthe system !at-hi-g-h frequencies, as may be passed-through capacitor 73, While notdecreasing the direct current gain, since the feedback path is blocked by capacitor 73 at direct current. The result of this additional feedback-path is the ability to raise the loop gain of the system-without encountering high frequency instability; This then insures-extreme staticaccuracy of the system. I

r If desired, the details of the power output stage of the main amplifier unit 26 as shown in FIG. 7 may be mod ified in the manner illustrated in FIG. 10. In this view it will be seen that a resistor 74 is insertedi-n series with the lead from the negative terminal of the power supply voltage to the emitter of output transistor 70. This is follo'wed by a capacitor 75 which maybe connected, as shown, to the common ground terminal. Alternatively, if preferred, capacitor 75' may be connected directly across resistor 74. A switch 76 is connected in parallel with resistor '74 so that the latter may be shunted out when its use is not desired. In a Similar manner, a resistor 77 is inserted in series with the lead from the terminal of the power supply voltage to the emitter of output transistor "ll. 7 by a capacitor 78 connected to the common ground terminal, and a switch 79 parallels resistor 77 to enable this resistor to be shunted out when desired.

The modified power output stage of H6. 10 functions in the following manner. Let it be assumed that switches 76 and 79'are open. If new slowly varying-signals are applied to the input terminal 29 to amplifier unit 26, then only a small amount of current need be drawn from the negative and positive power supply terminals, to flow through transistors '70 and 71 and out through the amplifie'r output terminal 28-t-othe galvanomete'r coil '19. Such small currents can be furnished continuously through resistors 74 and 77.'

Assume now, however, that 'a large, high frequency signal is applied to the amplifier inputterminal 29. The

rapid motion which is now called for by coil 19will require a considerable current to 'llowthrough the 'coil Resistors 74 and '77 are made 'suflici'e'ntly large that this current cannot be drawn through these resistors, but rather the current will be furnished by the storage capacitors '75 and 78 for 'a'period of'time,'until these capacitors have been discharged. This results inthe' high" frequency signal being recorded for only'a brief period of time, depending upon the discharge time of the capacltors. After the capacitors have been discharged, the" motion of coil 19 will be reduced to a low value, deter mined by the values of 'resistor's'7 4, 77. I

The purpose of the modification shown in FIG. 10 is to prevent rapid, largev amplitude motions of the recording stylus from occurring for a sustained period "of time.

Such large motions may be undesirable from the stand poi-nt'of damaging of theequipmenbor of causing unnecessary large spurious written'records in 're'spons'eto" undesired large'highfrequency input signals to the amp-lifier. Such signals may occur, for example, in bio-electric recording as the result of an electrode on the subject having become dislodged, and picking up random disturbances from the room. It is desirable, of course, that the records from 'such'disturbia'nces be minimized. The switches 76 and 77 are provided so that this feature of the recording apparatus may lie-eliminated when it is desired to record such rapidly varying phenomena.

In conclusion, the improved recording system in accordance with the invention has many advantages. The

This is followed recording itself is rectilinear and which is derived from a primary, signal produced motor force which is rotary, and the conversion from rotary to linear motion is obtained without the use of any mechanical linkage.

A further advantage is that the frictional force of the stylus against the tape, and of the contact member against the slidewire resistance, may be overcome by the large torque provided by the driving coil, which may be made very large for even a minute displacement from correct position.

Another advantage is that the proportionality of the position of the stylus, for a change in signal input voltage, is dependent only upon the uniformity of the slidewire, and does not depend upon any uniformity of magnetic field of the galvanometer, nor on other factors. Still another advantage of the invention is that, as contrasted with galvanometers employing a restoring spring associated with the movable coil, power need only be applied to the galvanometer coil when it is desired to shift the position of the stylus. The stylus will remain in any preset position, with no current flowing through the galvanometer coil.

While the foregoing embodiments of the invention are preferred ones for attaining the objects of the invention it is to be understood that various changes may be made in the construction and arrangement of the circuit components without, however, departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a recording oscillograph, the combination comprising a coil mounted for rotation about its axis, said coil being rotatable in a magnetic field in response to current passed through the coil, a stylus arm mounted with said coil for rotation therewith, a stylus assembly including a stylus element and an electrical contact member pivotally mounted on said stylus arm, a rigid rectilinear resistance member mounted transversely of a movable tape, spring means loading said stylus assembly against said rectilinear resistance member such that said contact member executes a rectilinear sliding movement across said rigid resistance member and said stylus element executes a rectilinear signal recording movement across said movable tape upon rotation of said coil and stylus arm, means including said resistance member for developing at said contact member a feedback voltage depending upon the position of said contact member on said resistance member, amplifier means, means connecting said feedback voltage and an input signal voltage in opposition at the input to said amplifier means, and means connecting said coil to the output from said amplifier means.

2. A recording oscillograph as defined in claim 1 and which further includes means developing an anticipatory component in said feedback proportional to the rotational velocity of said coil.

3, A recording oscillograph as defined in claim 1 and which further includes a capacitor connected in parallel with the means connecting said feedback voltage to the input to said amplifier means.

4. A recording oscillograph as defined in claim 1 wherein said pivot mounting for said stylus assembly includes a mounting arm pivotally connected to said stylus arm, and said spring means includes a compression spring having one end thereof seated in the outer end portion of said stylus arm and the opposite end bearing against said mounting arm so as to exert a force pushing said arm and said contact member of said stylus assembly into engagement with said resistance member.

5. A recording oscillograph as defined in claim 1 wherein said pivot mounting for said stylus assembly includes a mounting arm pivotally connected to said stylus arm, and said spring means includes a tension spring having one end thereof anchored to the outer end portion of said stylus arm and the opposite end anchored to said mounting arm so as to exert a force pulling said arm and said contact member of said stylus assembly into engagement with said resistance member.

6. In an electrical recorder, the combination comprising a coil mounted for rotation about its axis, said coil being rotatable in a magnetic field in response to current passed through the coil, a stylus arm mounted with said c-oil for rotation therewith, a stylus assembly including a stylus element and a contact member mounted on the outer end of said stylus arm and movable with respect thereto, a rigid rectilinear stationary guide member including a rectilinear electrical resistance-element thereon engaged by said contact member mounted transversely of a movable tape, and spring means loading said stylus assembly into resilient engagement with said rectilinear guide member such that said stylus element executes a rectilinear signal recording movement across said movable tape upon rotation of said coil and stylus arm and said contact member slides along said resistance element so as to vary the incircuit value thereof.

7. An electrical recorder as defined in claim 6 wherein said stylus assembly is pivotally mounted on said stylus arm by means which include a mounting arm pivotally connected to said stylus arm, and said spring means includes a compression type spring having one end thereof seated in the outer end portion of said stylus arm and the opposite end bearing against said mounting arm so as to exert a force pushing said mounting arm into engagement with said rigid rectilinear guide member.

References Cited by the Examiner UNITED STATES PATENTS 2,812,997 11/57 Diekmann et al. 346-117 3,088,788 5/63 Brown et al. 346117 LEO SMILOW, Primary Examiner. ROBERT L. EVANS, Examiner, 

1. IN A RECORDING OSCILLOGRAPH, THE COMBINATION COMPRISING A COIL MOUNTED FOR ROTATION ABOUT ITS AXIS, SAID COIL BEING ROTATABLE IN A MAGNETIC FIELD IN RESPONSE TO CURRENT PASSED THROUGH THE COIL, A STYLUS ARM MOUNTED WITH SAID COIL FOR ROTATION THEREWITH, A STYLUS ASSEMBLY INCLUDING A STYLUS ELEMENT AND AN ELECTRICAL CONTACT MEMBER PIVOTALLY MOUNTED ON SAID STYLUS ARM, A RIGID RECTILINEAR RESISTANCE MEMBER MOUNTED TRANSVERSELY OF A MOVABLE TAPE, SPRING MEANS LOADING SAID STYLUS ASSEMBLY AGAINST SAID RECTILINEAR RESISTANCE MEMBER SUCH THAT SAID CONTACT MEMBER EXECUTES A RECTILINEAR SLIDING MOVEMENT ACROSS SAID RIGID RESISTANCE MEMBER AND SAID STYLUS ELEMENT EXECUTES A RECTILINEAR SIGNAL RECORDING MOVEMENT ACROSS SAID MOVABLE TAPE UPON ROTATION OF SAID COIL AND STYLUS ARM, MEANS INCLUDING SAID RESISTANCE MEMBER FOR DEVELOPING AT SAID CONTACT MEMBER A FEEDBACK VOLTAGE DEPENDING UPON THE POSITION OF SAID CONTACT MEMBER ON SAID RESISTANCE MEMBER, AMPLIFIER MEANS, MEANS CONNECTING SAID FEEDBACK VOLTAGE AND AN INPUT SIGNAL VOLTAGE IN OPPOSITION AT THE INPUT TO SAID AMPLIFIER MEANS, AND MEANS CONNECTING SAID COIL TO THE OUTPUT FROM SAID AMPLIFIER MEANS. 